Some years ago processes were developed for producing a fibrous batt by contacting fibers with a dry fiber-binder based on certain thermoplastic polymers.
Such processes are described in the following US Patents among others:
Buck et al U.S. Pat. No. 3,993,518, "Buck '518"; and PA1 Buck et al U.S. Pat. No. 3,997,942, "Buck '942"; and PA1 Buck et al U.S. Pat. No. 4,047,991, "Buck '991"; and PA1 Buck et al U.S. Pat. No. 4,050,997, "Buck '997"; and PA1 Buck et al U.S. Pat. No. 4,051,294, "Buck '294"; and PA1 Buck et al U.S. Pat. No. 4,053,673, "Buck '673"; and PA1 Buck et al U.S. Pat. No. 4,053,674, "Buck '674" and PA1 Buck U.S. Pat. No. 4,211,817, "Buck '817"; and PA1 Buck et al U.S. Pat. No. 4,363,680, "Buck '680"; and PA1 Buck U.S. Pat. No. 4,550,050, "Buck '050"; and PA1 Buck U.S. Pat. No. 4,457,793, "Buck '793"; and PA1 Buck et al U.S. Pat. No. 4,473,428, "Buck '428"; and PA1 Buck U.S. Pat. No. 4,850,854, "Buck '854"; and PA1 Elsen U.S. Pat. No. 4,869,950, "Elsen".
These prior processes have proven very useful for a number of reasons. First, the noted processes can utilize inexpensive recycled fibers. Such fibers are recovered from garment clippings, textile mill waste and other waste fibrous products. These materials are sometimes referred to as "shoddy". Second, the patented processes are anhydrous, that is, completely dry, employing neither water nor solvent. Third, the fiber-binder employed is in its solid powdered form.
Batts produced by these prior processes find a wide variety of uses. They are useful as pads in mattresses, furniture, chairs and automobile seats. They are also useful as carpet underlay. In fact, these batts can be employed anywhere it is desired to provide resilience, thermal insulation, sound insulation and/or cushioning. These batts can be covered with other fabric or they may be visible to the naked eye. Said batts can be used almost everywhere that rubber or polyurethane foam have been used in the past. Such batts are, however, superior to foam for many reasons, particularly because they have a greater life under use. Because of their great utility these prior batts have achieved great commercial success. They are currently produced all over the world in quantities greater than about 25 million kilograms, about 25,000 tons, per year.
One disadvantage is the relatively high melting point of the thermoplastic resins used as fiber-binders. For example, a batt bonded with a dibutyl maleate copolymer must be heated to about 195.degree. C. (383.degree. F.). Such a high melting point is expensive to maintain because of energy costs. Such a high melting point increases the possibility of adverse heat effects on components of the batt. The higher the melting point of the thermoplastic resin in the fiber-binder, the greater the danger that it or other components of the batt will catch fire.
Unfortunately these prior batts and processes for their production suffer from a number of disadvantages. Batts bonded with fiber-binders of chlorine-containing thermoplastic resins suffer from a number of disadvantages. These chlorine-containing resins employ polymers which include vinyl chloride and/or vinylidene chloride. In these batts, a danger exists that an undesirable release of hydrochloric acid will occur. This hydrochloric acid causes a number of problems in both processes for producing the batts and in methods of using the resultant batts because hydrochloric acid, which is toxic and highly corrosive, must be contained in the process apparatus. Such apparatus must be constructed with an airtight enclosure and with a fan to keep the enclosure under a negative air pressure. If the apparatus is opened for inspection, adjustment or repair, workers may be exposed to the HCl toxic vapors. The vapors escaping from the unit must be contained. Repair costs are increased because of the hydrochloric acid. Provision must be made to safeguard workers. The hydrochloric acid must be neutralized, usually with caustic (NaOH) or lime (CaO), producing as neutralization products respectively impure salt (NaCl), and impure calcium chloride (CaCl.sub.2). These neutralization products must be disposed of in a manner consistent with a proper regard for the environment. Such disposal is expensive, but vital. Some environmentalists have suggested that a relationship exists between chlorine and the presence in the environment of dioxin.
While the chlorine in these chlorine-containing batts tends to make the resultant batts somewhat fire resistant, chlorine alone is frequently insufficient. It has become common practice to improve the fire resistance of the batts by the addition of antimony oxide, boric acid, diammonium phosphate and/or aluminum trihydrate. Unfortunately, such added materials tend to increase the propensity of the chlorine-containing fiber-binder to decompose with a resultant undesirable release of hydrochloric acid. This hydrochloric acid must be captured and scrubbed from the effluent stacks to prevent undesirable air pollution. The amount of hydrochloric acid released during curing of the batt increases sharply at temperatures above 205.degree. C. (400.degree. F.). The effluent by-products produced during batt curing may produce effluent opacities above acceptable limits. Expensive emission control devices are required for monitoring and control.
After formation of these prior batts with white fibers and chlorine-containing resins, yellowing of the fibers may occur. Where the fibers are visible, consumer demand is diminished.
The prior batts produced with chlorine-containing fiber-binders, when used in upholstery with steel springs, are believed to catalyze rusting of the springs. This can result in undesirable squeaking of the springs.
Batts bonded with chlorine-containing resins have been rejected for use as padding for seats and panels in automobiles. Automobile manufacturers fear that any hydrochloric acid release would damage the printed circuits that are part of the computer and electronic components of modern autos.
Many of the prior batts bonded with thermoplastic resins give off a gummy vapor when heated. This gummy vapor appears to come from plasticizers which have been mixed with the resin. Examples of plasticizers are dioctyl phthalate and epoxidized soy bean oil. During the heating process these plasticizers are released. The plasticizers can condense as oily residue on top of the neutralization solution, making disposal expensive. They can also condense as a gummy residue which may ignite in oven exhaust causing fires. Removing this residue is time consuming and expensive.
One automobile manufacturer has promulgated an empirical test to measure the suitability of batts for use as padding under the carpet of automobiles. In this empirical test, a sample of the batt is exposed to a temperature of 232.degree. C. (450.degree. F.) for a period of one hour to simulate heating through the automobile floor by the catalytic converter. After the heating period, the pad is examined to determine whether (1) it has produced any odor, (2) it has discolored and (3) it has lost its shape. The prior batts bonded with chlorine-containing fiber-binders fail this test.
As described in the prior art, these prior thermoplastic binders must be utilized in the form of small particles. One method is to polymerize monomers producing directly a resin of the desired particle size. The high cost of this method makes it commercially impractical. A less expensive method is to form the resin without regard to particle size and then grind it to the desired size. Unfortunately, some of these prior thermoplastic binders are relatively soft and require very long grinding times to achieve the desired particle size. Because of their softness the particles tend to deform rather than fracture. Grinding at cryogenic temperatures is of limited success, but is expensive.
In recent years the cost of all the noted prior thermoplastic fiber-binders has increased dramatically. This increase has resulted in increased costs for products employing such prior batts, leading to the substitution of other, inferior, less expensive products.
A great deal of effort has been expended in attempting to reformulate these resins economically to lower their melting points. Unfortunately, these attempts have met with only very limited success. In one attempt, a copolymer of vinylidene chloride and vinyl chloride was converted to a terpolymer by introducing other vinyl monomers, such as vinyl acetate and dibutyl maleate. It was believed that the resultant terpolymer would have a melting point lower than that of the copolymer. In another attempt, mixtures or alloys of two or more thermoplastic resins were employed. An attempt to use polyolefins was unsuccessful because of difficulty in grinding and the propensity of the polyolefins to produce, during grinding, fibers rather than small particles.
More recently some success has been achieved when the prior thermoplastic fiber-binder is contacted with the fibers of the batt by blowing it through a fully formed batt. However the thickness of such a batt is limited to about 5 cm (2 inches) because of the tendency of the thermoplastic fiber-binder to fail to penetrate the batt fully. Increasing the air speed through the batt has been only partially successful. As a result, such process is limited to those employing preformed batts of less than 7 cm (3 inches).
These prior batts can be cold molded but cannot be hot molded. In the cold molding process, the batt is heated and placed in a cold mold until the batt cools to the temperature of the mold. In the hot molding process, the batt is placed in a hot mold. After a certain time, the batt is removed from the hot mold. A demand exists for batts which can either be hot molded or cold molded.
A completely unrelated, non-analogous field of electrostatic coating also has a number of problems related to the disposal of waste coating powders. In this field, the substrate to be coated, which may be an automobile body, is given an electrical potential different from a powder spray gun. Coating powder is projected through said gun in a gas stream toward the substrate. Some of the coating powder does not adhere to the substrate and is collected as scrap. A portion of the powder, which is entrained in the air, is then recovered in filters as scrap. Much of this scrap cannot be reused without adversely affecting the resultant coatings. The scrap must be disposed of in an environmentally responsible manner. The disposal of this scrap is a burden on the coating factory. Some factories burn the scrap, whereas others pay to have it transported to an acceptable land fill. Today, millions of pounds of scrap material are injected into the environment annually. If the scrap is burned a danger exists of contributing to air pollution. If the scrap is placed in a land fill a danger exists of contaminating drinking water sources.
Other "off-grade" or scrap material is available from the manufacturer of the coating powder because of defects, poor color and/or the presence of contaminants that make the material unsuitable for use in the powder coating industry. Such material poses a similar disposal problem.